Power drive units for aircraft cargo handling systems conventionally include a drive roller coupled to an electric motor for engaging and propelling cargo along a ball or roller conveyor surface to and from storage positions within an aircraft hull. Self-erecting power drive units are particularly advantageous in many aircraft cargo handling system applications. In these units, application of electrical power to the drive motor initially operates to raise the drive roller from a lowered or retracted position beneath the conveyor surface to a raised or erected position in which the drive roller is disposed at the cargo conveyor plane for engagement with the cargo units.
In both stationary and self-erecting units, the output of the motor is conventionally coupled through planetary gear systems to an output gear coaxial with the motor, and then through idler gears to the drive roller and roller-erecting mechanism where applicable. The planetary stage output gear is conventionally supported by bearings against reaction forces applied thereto by the idler gears from the drive roller. It is a general object of the present invention to provide a power drive unit of the described character in which such output gear support bearing is eliminated, thereby resulting in a more compact construction in which the output gear stage is free-floating and self-aligning in operation. It is thus a related object of the present invention to provide a power drive unit of the described character that is more compact, reliable and rugged than are comparable units in the prior art.
A power drive unit for aircraft cargo handling systems in accordance with the present invention includes a motor and a drive roller carried for engagement with cargo to be driven by the unit. Planetary gears rotatably couple the output shaft of the motor to an output gear, which preferably is coaxial with the motor output shaft. Idler gears extend laterally from the planetary output gear and rotatably couple the planetary output gear to the roller drive shaft. One or more angularly spaced reaction gears are coupled to the planetary output gear in opposition to the idler gears for supporting the output gear against reaction forces imparted thereto by the drive roller through the idler gears.
In the disclosed embodiment of the invention, the reaction gear or gears comprise idler gears mounted on associated adjustable eccentric shafts. The eccentric shafts have screwdriver slots or other suitable means at one end, and are held in adjusted position by set screws threadably received in the unit housing. It would be preferable, for reasons of cost, to eliminate the need for gear and shaft adjustment. The roller output shaft in the preferred embodiment of the invention is mounted for rotation in stationary position within the unit housing. The roller drive shaft is coupled by gears to the surrounding drive roller in such a way that the drive roller orbits around the drive shaft. Locators extend from the drive roller and are received in arcuate slots in the unit housing. In this way, initial energization of the drive unit motor operates through the roller drive shaft and gears to raise the roller into a cargo-engaging position, with motion thereof being guided by the locators received in the arcuate slots. Further rotation of the drive motor functions to hold the roller in the raised position while rotating the roller about its axis.